The current System 80+ Feedwater Control System (FWCS) automatically controls the feedwater flow to the steam generators between 5% and 100% power. However, feedwater control below 5% power is a manual operation. The current FWCS uses input signals of steam flow rate, feedwater flow rate, and steam generator level to develop output signals that control the position of the feedwater valves and the speed of the feedwater pumps.
There is a large economizer feedwater valve, a small downcomer feedwater valve and a very small startup feedwater valve. The startup feedwater control valve is located in parallel with the downcomer feedwater valves. The large economizer feedwater valve is automatically controlled by the above three signals of the FWCS between 20% and 100% power. Also, the small downcomer feedwater valve is automatically controlled by only the steam generator level signal of the FWCS between 5% and 20% power. Furthermore, the very small startup feedwater valve is manually controlled by an operator when the power level is between 0% and 5%.
It is an object of the present invention to simplify the FWCS design, to make the system more reliable, and to reduce its capital operating cost, which previously had two automatically functioning systems, and one manually functioning system, according to the existing power levels. It is another object of the present invention to provide a more reliable feedwater system than is currently provided, especially with the System 80+ Feedwater Control System, by extending the operating range of the existing small downcomer valve and the larger economizer feedwater valve. It is another object of the invention to increase the automatic feedwater control operating range down to zero percent power, thereby relieving operators of monitoring and operating of the FWCS at operation power levels below 5%.